This invention relates to the pretreatment of catalytic absorbents employed in non-hydrogenative hydrocarbon processing, and particularly, to a method for removing water from a catalytic absorbent prior to the absorbent being employed in a process for desulfurizing a hydrocarbon feedstock.
Hydrocarbon refining processes such as catalytic reforming are utilized for such purposes as dehydrogenation, hydrogenation, cyclization, dehydrocyclization, isomerization and dehydroisomerization of selected hydrocarbons. Catalytic reforming processes play an integral role in upgrading straight run or cracked naphtha feedstocks, as by increasing the octane number of the gasoline fraction contained in such feedstocks. In a typical reforming process treating a straight run naphtha or cracked naphtha, the feedstock is upgraded by contact with a catalyst comprising a noble metal on alumina, and more particularly, noble metal catalysts containing hydrogenation promoters such as rhenium and cracking promoters in the alumina such as chlorine. Conditions utilized in reforming processes vary depending upon such factors as the type of feed processed and the desired increase in octane level.
To achieve maximum run lengths and increase process efficiency, it is generally recognized that the sulfur content of the feedstock must be minimized. Reforming catalysts, and particularly those comprising platinum, and most particularly comprising platinum, rhenium and chlorine, are poisoned and, in effect, deactivate rapidly, in the presence of sulfur compounds. As a result, it is necessary to reduce the sulfur content of reformer feedstocks as low as possible, and preferably, feedstocks contacted with reforming catalysts are desulfurized to contain less than 0.1 ppm by weight sulfur.
A common method of treating reformer feeds to reduce the sulfur content is by hydrodesulfurization wherein a naphtha or other hydrocarbon is contacted with a sulfur-tolerant hydrogenation catalyst in the presence of hydrogen. The sulfur in the hydrocarbon is converted to hydrogen sulfide, which may be separated from the naphtha by conventional means prior to reforming. Although highly effective sulfur removal may be achieved by hydrodesulfurization units operating under severe conditions, the efficiency of such processes is ultimately limited by equilibrium and/or kinetic considerations. In many instances, it is not possible to obtain hydrodesulfurized products containing less than 0.1 ppmw sulfur as desired in most reforming operations. Furthermore, it is impossible to guard against upsets in the hydrodesulfurization unit which can result in high levels of organosulfur compounds remaining in the reformer feedstock.
In addition to hydrodesulfurization, there are other methods employing catalytically active materials for removing sulfur from hydrocarbons. One such method reduces the sulfur content of the hydrocarbon by "absorbing" sulfur onto a catalytically active absorbent material under non-hydrogenative conditions, i.e., conditions involving contact of the absorbent material with a hydrocarbon essentially in the absence of free hydrogen. Usually, the absorbent material contains a metal component, such as nickel, copper or silver, supported on a porous refractory oxide, and the feedstocks generally treated are reformer feedstocks, particularly naphthas. Typical of such processes include the process disclosed in U.S. Pat. No. 2,767,759 to Annable wherein a bed of nickel molybdate pellets is utilized to reduce the sulfur content of naphthas. Similarly, in U.S. Pat. No. 4,204,947 to Jacobson et al., the use of copper components supported on conventional carriers is disclosed for reducing the thiol content of naphthas by absorption. In addition, Thorn in U.S. Pat. No. 2,876,196 describes a method for desulfurizing hydrocarbon feedstocks by contact with catalytic particles comprising platinum supported on a suitable carrier. The metallic components of such catalytic absorbents are effective for their intended use in either an oxidized or reduced form, depending upon the particular catalytic absorbent.
In some cases, the catalytic absorbent accumulates physically absorbed water on its surface prior to being employed for its intended use. Accordingly, there is a need to provide a method for drying a catalytic absorbent prior to placing it onstream for hydrocarbon processing.
Furthermore, there is a need to provide a method for drying a catalytic absorbent, while still maintaining the effective form of the metals supported on the absorbent.
Another object of the invention is to provide a method for removing accumulated water from a catalytic absorbent, and more particularly, to remove water from a catalytic absorbent prior to the absorbent's use in a hydrocarbon processing scheme.
It is another object of the invention to provide a method to protect a reforming catalyst that is susceptible to damage and/or deactivation due to contact with too much water.
More particularly, it is an object of the invention to provide a convenient method for drying a catalytic absorbent employed in a non-hydrogenative desulfurization process of a naphtha-containing hydrocarbon feedstock located upstream of a catalytic reformer processing unit that requires the presence of hydrogen.
These and other objects and advantages of this invention will become apparent to those skilled in the relevant art in view of the following description of the invention.